How Can I Tell If Gypsum Is Working?

I have been interested in gypsum for nearly a decade now and we have applied it on our family farm in Nebraska – following a 3 year cycle with 1 ton applications every third year. I had heard all the stories how it improves soil structure, particularly in tight clay soils with high soil density. Of course as an agronomist I also knew that change would not come overnight. We were dealing with soils that have been farmed conventionally for a 100 years. And what took 100 years to change can’t be remedied in one year. But I knew that with time and the right complementary practices, the soil could change and would change relatively fast.

For those that regularly read my blog, you know by now that gypsum provides two main benefits: it is an amendment that improves soil and provides nutrients to feed plants and soil microbes.  And although each field is different, in general gypsum can be applied at a rate of 200 to 400 lbs per acre annually or a ton per acre every 3 or 4 years. As a soil amendment change takes time but as a nutrient source crops can benefit that season of application.

But how did I know it if is really working? Do you take it on faith alone that it works or are there things you can measure or observe?  The answer is a combination of measuring results with data and getting out in the field to dig, feel, and observe.

Measure, Observe     

Take a soil sample before and after application and measure the amount of soluble calcium available to plants. Calcium ties up in the soil, either on the exchange complex or with carbonate. While soils contain abundant levels of calcium, much of that is not readily available so an application of gypsum will increase soluble calcium levels in the soil.

Take a soil sample and measure the amount of sulfur available. Sulfur is a very fleeting nutrient in nature, is mineralized from organic matter, taken up by plants or microorganisms or lost to the ravages of nature. In the past, sulfur came from organic matter and atmospheric deposition based on sulfur emissions. Today it only comes from organic matter so soils are often low in sulfur and supplementing sulfur is an increasingly important management practice.

Get out the spade; dig, look, feel and smell. Compare a treated soil to an untreated soil. How easily can you push the spade in the soil, how easily does the soil break apart in your fingers, does it smell earthy and healthy? While measurements will validate change nothing is more powerful that seeing it with your own eyes and feeling it with your fingers.

Take a sample of undisturbed soil in your hand and look at it and examine its structure. Is it structure-less with only fine material like sand or is it massive and aggregated together tightly into blocks or is it granular and crumbly? Take a large clump of soil and put it in water to see how fast it disperses. You can also assemble some aluminum or iron tubes 8-inches long and four inches in diameter and measure bulk density and water infiltration.

Add in compost and cover crops, as I did and you bring in the glue that cements these aggregates together and gives them resiliency against the threats of nature and impacts of farming. After about three years I could take a spade and dig into the soil and notice the change in density and structure. And while walking across the field I could feel how spongy the soil surface felt and after 10 years that change is dramatic.

If you want to know for yourself if gypsum works, get out and dig, feel and measure. You will record change.

Author: Dr. Daniel Davidson

Dr. Daniel Davidson – EcoGEM Agronomist.  Dr. Daniel Davidson is a nationally recognized agronomist.  He served most recently as Director of Strategic Research for the Illinois Soybean Association.  Dr. Davidson has also served in various capacities at GEOSYS, Cargill, Agri Business Group and Agri Growth, Inc.  He holds a Ph.D. in Agronomy from Washington State University and an MS in Agronomy from the University of Missouri.

Dr. Davidson posts articles on soil health and management related subjects. If you have suggestions for topics or questions, feel free to contact him at or call 402-649-5919.